
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <!DOCTYPE html>
    <html lang="en">

    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>
        <script src="https://cdn.jsdelivr.net/npm/vue@2.6.14/dist/vue.js"></script>
    </head>

    <body>
        <div id="root">
            姓：<input type="text" v-model="firstName"><br /><br />
            名：<input type="text" v-model="lastName"><br /><br />
            姓名：<span>{{fullName}}</span>
        </div>
        <script>
            const vm = new Vue({
                el: "#root",
                data: {
                    firstName: '张',
                    lastName: '三',
                    fullName:'张-三'
                },
                // computed: {
                //     //简写
                //     fullName() {
                //         return this.firstName+'-'+this.lastName
                //     }
                // },
                watch:{
                    firstName(val){
                        this.fullName = val+'-'+this.lastName
                    },
                    lastName(val){
                        this.fullName =this.firstName +'-'+ val
                    }
                }
            })
        </script>

    </body>

    </html>
</body>

</html>